1. Field of the Invention
The present invention relates to a reflection type projection display apparatus in which red, green, and blue image lights respectively coming from reflection type spatial light modulation elements (reflection type liquid crystal panels) respectively for red, green, and blue light are reflected by wire grid polarizers respectively for red, green, and blue light; unwanted polarization component is excluded therefrom; and then the image lights are color-combined by a color combination optical system to be projected on a projection plane (for example, a screen) by a projection lens. Specifically, the present invention relates to such a reflection type projection display that is capable of correcting lateral chromatic aberration on the projection plane.
2. Description of the Related Art
A projection display apparatus for projecting color image in magnification can be categorized into various types depending on its configuration, specifically, an arrangement of constituting optical components. Typically, there are two types—one is a transmission type projection display apparatus and the other is a reflection type projection display apparatus. In the former, light to be projected passes through a spatial light modulation element using a liquid crystal panel, whereas in the latter the light is reflected by the spatial light modulation element. In both types of apparatus, white light emitted from a light source is color-separated into red (R) light, green (G) light, and blue (B) light by a color separation optical system; the lights of the three primary colors are guided to liquid crystal panels respectively for R, G, and B light to be optically modulated into image lights of R, G, and B color; the image lights are color-combined into a color-combined image light by a color-combination optical system; and the color-combined image light is projected in magnification on a screen by a projection lens.
When the color-combined image light produced by color-combining image lights of R, G, and B colors using the color-combination optical system is projected by the projection lens, since the wavelengths of the color-combined image light are in a range from blue to red color region, namely, cover from 400 nm to 700 nm, and a magnifying power of the projection lens is different depending on the wavelength, a lateral chromatic aberration takes place on the screen.
Lateral chromatic aberration can be corrected by designing the projection lens. However, such designing is rather expensive and, besides, the lens has to be fabricated with an expensive glass material, thereby leading to an increased production cost. In order to solve such a problem inexpensively, there has been proposed a projection display apparatus which is provided with a plus or minus correction lens means above part or all of image forming surface of a plurality of liquid crystal devices (light valve) so as to reduce the lateral chromatic aberration on the screen (See, Japanese Patent No. 2867529).
FIG. 1 is a schematic view of a related art projection display apparatus. FIGS. 2A and 2B are an explanatory view for explaining the reason how a lateral chromatic aberration takes place on a screen when R, G, and B lights are projected by a projection lens in the related art projection display apparatus.
The related art projection display apparatus 100 illustrated in FIG. 1 has been disclosed in the above publication and will be described briefly here referring to the publication.
As illustrated in FIG. 1, white light emitted by a white light source 101 is incident upon a dichroic mirror 102 that reflects R (red) light and allows G (green) light and B (blue) light to pass therethrough.
The R light is reflected by the dichroic mirror 102 to change its proceeding direction by 90 degrees and thus to reach a reflection mirror 103. Next, the R light is reflected by the reflection mirror 103 to change its proceeding direction again by 90 degrees. Then, the R light reaches to a liquid crystal light bulb 105R for R light after passing through a condenser lens 104R for R light, and is optically modulated by the liquid crystal light bulb 105R in accordance with an image signal to become R image light. Furthermore, the R image light passes through a plus correction lens 106 and then a dichroic mirror 107.
On the other hand, the G light and the B light that have passed through the dichroic mirror 102 are incident upon a dichroic mirror 108 that reflects the B light and allows the G light to pass therethrough. The B light that is reflected by the dichroic mirror 108 to change its proceeding direction by 90 degrees reaches a liquid crystal light bulb 105B after passing through a condenser lens 104B for B light. The B light is optically modulated by the liquid crystal light bulb 105B in accordance with an image signal to be B image light. Then the B image light passes through a minus correction lens 109 and is reflected by a dichroic mirror 107. Here, the aforementioned R image light and the B image light are combined by the dichroic mirror 107 and the combined light passes through a dichroic mirror 111.
On the other hand, the G light that has passed through the dichroic mirror 108 proceeds through a condenser lens 104G for G light and a liquid crystal light bulb 105G in this order. The G light is optically modulated to become G image light by the liquid crystal light bulb 105G and then reflected to change its proceeding direction by 90 degrees by a reflection mirror 110 to be incident upon the dichroic mirror 111. Then, the G image light is reflected and color-combined with the aforementioned R and G image light by the dichroic mirror 111. Finally, the color-combined light produced by color-combining the three image lights is projected on a screen 113 in magnification by a projection lens 112.
As illustrated in FIG. 2A, when the color-combined image light produced by color-combining the R, G, and B image lights is projected on the screen 112 in magnification by the projection lens 112 that is composed of a plus correction lens 112a, an aperture 112b, and a minus correction lens 112c, all of which are arranged in this order from the light incident surface to the light exit surface, a refractive index of the projection lens 112 is varied depending on the wavelength of the R, G, and B light component. Namely, the B light component is refracted to a greatest extent and the R light component is refracted to a least extent. Therefore, an image forming magnification becomes lower in the order of the B, G, and R light component.
As illustrated in FIG. 2B, due to such a difference, the B light component is focused at a position furthest away from the screen center and the B light component is focused at a position nearest to the screen center compared with the focused G light on the screen 113. This is how lateral chromatic aberration takes place on the screen 113.
Therefore, in the above projection display apparatus 100 of the related art, while the G light component among the R, G, and B components is set as reference, the plus correction lens 106 is provided adjacent to the exit surface of the liquid crystal light bulb 105R for R and the minus correction lens 109 is provided adjacent to the exit surface of the liquid crystal light bulb 105B. With this configuration, the R, G, and B light components of the color-combined image light are all focused on one point on the screen 113 as white light. This is how the lateral chromatic aberration is corrected on the screen 113.
By the way, although a drawing is omitted, here the publication also discloses that when the projection lens is composed of a minus lens, an aperture, and a plus lens in this order from the incident surface to the exit surface thereof, the image forming magnification becomes lower in the order of the R, G, and B light component, which is an opposite order in the above.
In the above projection display apparatus 100, it is since a correction lens means such as the plus correction lens 106 or the minus correction lens 109 is provided so as to be positioned between all or part of the image forming surface of the liquid crystal devices (the light bulbs) 105R, 105G, 105B and the projection lens 112 along the light path that the lateral chromatic aberration can be corrected. Although this configuration is well suited to correct the lateral chromatic aberration on the screen for a projection display apparatus that employs the transmission type liquid crystal devices (the light bulbs) 105R, 105G, 105B, it is somewhat disadvantageous in terms of resolution of the image projected on the screen.
Therefore, there has been desired a reflection type projection display apparatus that is able to efficiently correct the lateral chromatic aberration on an projection plane (for example, a screen) when a wire grid polarizer having an excellent polarizing properties respectively for R, G, and B lights emitted from a reflection type spatial light modulation element (a reflection type liquid crystal panel) that is capable of improving resolution in a reflection type projection display apparatus employing a reflection type spatial light modulation element.